1. Field of the Invention
This invention relates to Asynchronous Transfer Mode packet switching, and more particularly to an improved recovery system to reroute data in the event of a link failure.
2. Description of the Prior Art
As will be appreciated by those skilled in the art, telecommunication networks around the world are implementing systems based on standards established and known in the art as the Broadband Integrated Services Digital Network (B-ISDN). Within an B-ISDN system, data is transferred in a high-speed network from source to destination through a series of interconnected nodes. Within the B-ISDN specification a specifically defined packet orientated transfer mode is commonly used, called "Asynchronous Transfer Mode (ATM)". This is an asynchronous multiplexing operation, with the multiplexed information flow organized in fixed size blocks, called cells. Current trends in standardization of the ATM transport format favor a cell size that has a 48-byte information field and a 5-byte header.
Prior to launching a cell, a virtual path is established and dedicated for the cell transmission through the various nodes in the system. The cell header includes the source and routing information and each node has a routing table that, based upon the routing information, routes the cell between an input link upon which the cell arrived and a proper output link in accordance with the cell header and routing information.
Nodes in an ATM system are commonly interconnected by high-speed communication links, such as a full duplex telephone T3 link with a DS3 specified format. Several other communication links such as T.sub.1, OC3, OC12 and the like can be used. The invention is not limited to a specific link. If a communication link between nodes is broken or faulty, an alternate route for cells assigned to the broken or faulty link must be immediately established. There have been a number of prior art proposals for re-routing cells in the presence of a faulty or broken communication link between switching nodes. One that is attractive, in terms of recovery speed, provides dedicated spare communication links and spare circuits within the node, which are used in the event of a communication link failure between nodes. This approach, while satisfactory in terms of result, is costly in that it requires spare equipment and communication links. In addition, such prior art systems are complex in terms of system administration.